Iconic Mojave Joshua trees in race against extinction
By HENRY BREAN
LAS VEGAS REVIEW-JOURNAL
A century from now, the Mojave Desert’s iconic plant could be pushing its way into new territory or teetering on the brink of extinction.
This spring, a pair of researchers will go looking for clues to the Joshua tree’s fate in a lonesome valley 140 miles north of Las Vegas. And they’re inviting interested “citizen scientists” to join them in their search.
Henderson-based ecologist Todd Esque, from the U.S. Geological Survey, and evolutionary biologist Chris Smith, from Willamette University in Salem, Ore., are offering a four-day course in March called “The Race North: Population Ecology of Joshua Trees In an Era of Climate Change.”
The class will unfold in Tikaboo Valley, near the Lincoln County town of Rachel, where Smith said Joshua trees seem to be “experiencing something of a population boom” at the northern limit of their current range, possibly in response to increasingly warmer, drier conditions to the south.
Such research matters, Esque said, because it could help scientists predict how much of a challenge climate change will pose for Joshua trees and for people. “We’re all in this together,” he said.
“Any time these large climatic events occur, some things blink out and some things survive and create new species,” he said. “If Joshua trees can respond quickly enough and spread their seeds far enough with each jump, they will continue to thrive out there.”
“It’s a population on the move as far as I’m concerned.”
Some computer models predict the Joshua tree could disappear from much of the Mojave Desert, as average temperatures rise and droughts grow longer and more frequent.
Smith said scientists have found evidence that the trees are already fading from parts of Joshua Tree National Park at the southern end of its range.
Tikaboo Valley serves as an ideal “natural laboratory” for studying the species because that’s where the two main varieties of Joshua tree — one from the east, the other from the west — come together and mix.
“It is possible to do a side-by-side comparison of which of the two plants are likely to win ‘The Race North,’ and how the reliance on specialized pollinators might limit their capacity to escape changing climate,” Smith said in an email.
This is his area of expertise. Smith has spent the past decade studying the highly specialized evolutionary bond between the Joshua tree and the tiny moth that pollinates it.
Each spring, yucca moths emerge from the ground to mate and lay eggs in the flowers of Joshua trees in Nevada, California and Arizona. But unlike bees and other insects that inadvertently spread pollen from flower to flower, these moths appear to deliberately pollinate Joshua trees so that the plants will produce seeds that eventually will feed the moth’s caterpillars when they hatch.
Simply put, the Joshua tree would not exist without the plain-looking moth about the length of a pencil eraser, and the moth would not exist without the tree.
Smith is studying how natural selection is involved in shaping this tight relationship between plant and insect — and whether their bond can live through climate change and the tree’s own race for survival. Last year, he received a prestigious, $850,000 grant from the National Science Foundation to continue his research for the next five years at least.
For his part, Esque has spent 10 years trying to produce the first comprehensive understanding of the tree’s life history. Along the way, he has amassed one of the most complete sets of data about where the trees occur and co-authored a study showing that only the largest, oldest Joshuas tend to survive wildfires — a finding Smith called “worrying” since fires have become more common in the Mojave Desert.
This marks the second time Smith has hosted a citizen science expedition to the Tikaboo Valley. He offered a similar class last year, minus the emphasis on climate change.
Registration is now underway for the course, which is being sponsored by the Desert Institute at Joshua Tree National Park in California. It takes place March 21-24 and costs $260, not including food, lodging, supplies and transportation to and from Tikaboo Valley.
Esque said the class will begin with a lecture on “why are we here and why does it matter.” Then the group will divide up into teams and walk the valley with GPS units, measuring trees and collecting genetic samples.
On the final day, Smith, Esque and their students will discuss what the collected data might tell them about the Joshua tree’s march north through Nevada and whether the species can survive long enough to get wherever it’s going.
